Fuel injection system control method

ABSTRACT

A method of controlling a dual fluid fuel injection system of an internal combustion engine having at least one cylinder, the fuel injection system having at least one delivery injector and a compressed gas supply means for supplying gas to the at least one delivery injector, the method including: 
     determining if there has been a reduction in the compressed gas supplied to the at least one delivery injector below a required supply level; 
     opening the at least one delivery injector when there is a depression in a respective said cylinder such that the pressure within said cylinder is lower than the pressure upstream of the delivery injector if the compressed gas supply is below said required supply level; and 
     delivering fuel to the delivery injector such that the fuel is drawn into the cylinder by virtue of the pressure differential existing across the delivery injector.

The present invention is generally directed to dual fluid fuel injectionsystems for internal combustion engines, and in particular to a methodof controlling such dual fluid fuel injection systems.

The Applicant has developed dual fluid fuel injection systems for use ininternal combustion engines wherein metered quantities of fuel areinjected into the combustion chamber(s) of an engine, entrained in acompressed gas. An example of such a system is described in theApplicant's U.S. Pat. No. 4,934,329, the details of which areincorporated herein by reference. Such systems require a source ofcompressed gas such as an air compressor to operate properly. Thecompressed gas is supplied to the delivery or air injectors of the fuelinjection system which deliver fuel into the engine. Typically, separatefuel supply means supply metered quantities of fuel to each deliveryinjector and the compressed gas entrains and delivers the fuel to theengine when the delivery injector is opened. Such air-assisted fuelinjection has been shown to promote improved fuel spray formation anddistribution within the combustion chambers of the engine, leading tobenefits such as improved emissions, fuel economy and engine operatingstability.

However, the gas supply upon which the dual fluid fuel injection systemis reliant can be lost if for example there is a mechanical failure ofthe air compressor or a break or significant leak in the air supplysystem between the air compressor and the delivery injectors of the dualfluid fuel injection system. Such a loss of the compressed gas supply tothe delivery injectors will prevent the dual fluid fuel injection systemfrom operating properly resulting in unsatisfactory engine operation orin fact thereby disabling the engine. That is, no, or an unsatisfactoryquantity of compressed gas will be available at each delivery injectorto entrain and deliver fuel into the combustion chambers of the engine.

It is therefore an object of the present invention to provide a methodof operating a dual fluid fuel injection system if there is such adisruption of the compressed gas supply to the delivery injector.

With this in mind, there is provided a method of controlling a dualfluid fuel injection system of an internal combustion engine having atleast one cylinder, the fuel injection system having at least onedelivery injector and a compressed gas supply means for supplying gas tothe at least one delivery injector, the method including:

determining if there has been a reduction in the compressed gas suppliedto the at least one delivery injector below a required supply level;

opening the at least one delivery injector when there is a depression ina respective said cylinder such that the pressure within said cylinderis lower than the pressure upstream of the delivery injector if thecompressed gas supply is below said required supply level; and

delivering fuel to the delivery injector such that the fuel is drawninto the cylinder by virtue of the pressure differential existing acrossthe delivery injector.

The term “cylinder depression” refers to the condition where thepressure within the cylinder is lower than a reference pressure, in thiscase, the pressure upstream of the delivery injector.

The delivery injector(s) may inject fuel directly into a respective saidcylinder. In the case of a multi-cylinder engine, each cylinder may beprovided with a respective said delivery injector.

Conveniently, the compressed gas supply means comprises an aircompressor and air supply means for communicating the output of the aircompressor with the delivery injector(s) of the fuel injection system.The reduction in the compressed gas supplied to the at least onedelivery injector may typically be constituted by an interruption of thecompressed gas supply from the air compressor. Alternatively, thereduction may arise due to a failure, break or leak within the airsupply means communicating the compressor with the delivery injector(s).

The method according to the present invention may control the durationof opening of the delivery injector. Alternatively or in addition, thestart of opening of the delivery injector may be controlled.

Preferably, the start of opening and duration of opening of a saiddelivery injector of a said cylinder of the engine occurs when thecylinder is undergoing an intake stroke therein. Preferably, fuel isdelivered to the delivery injector at least in the period when thedelivery injector is opened.

Conveniently, the delivery injector is actuated by way of anelectromagnetic solenoid such that, even though the source of compressedgas may have been interrupted or reduced, the delivery injector maystill be operated to provide communication with a cylinder of theengine. Such electromagnetic control is well known in the field of fuelinjection systems. It should however be noted that other suitable formsof delivery injector may also be used in accordance with the presentinvention.

The present invention relies on there being a lower pressure within thecylinder when the delivery injector is opened. As is well understood,when a piston within the cylinder is moving towards bottom dead centreon the intake stroke thereof, a vacuum is created within the cylinder.The vacuum induced in the cylinder during the intake stroke helps todraw the fuel held within or being supplied to the delivery injectorinto the cylinder whilst the delivery injector is held opened. This isbecause a pressure differential is created across the open deliveryinjector which enables a net mass flow of fluid from the deliveryinjector into the cylinder. This ensures that sufficient fuel is drawninto the cylinder to sustain the subsequent combustion event in thecylinder.

Depending on the timing of the opening of the delivery injector andhence the level of the pressure differential across the open deliveryinjector, sufficient air may be drawn from upstream of the deliveryinjector to still provide a desirable level of atomisation andentrainment of the fuel. That is, air may be drawn through the failedair compressor or the air supply means, and through the deliveryinjector to assist with the delivery of the metered quantity of fuelinto the cylinder in the normal manner. This may of course depend on thetype of failure or leak upstream of the delivery injector, however,measures may be adapted to ensure that air is able to be drawn throughthe delivery injector under such situations. For example, air may bedrawn from another cylinder of the engine whose delivery injector isalso controlled to be open.

Conveniently, the fuel may be delivered to the delivery injector duringthe period when the injector is opened. This may, for example, be thepreferred timing at relatively low loads of the engine. However, as theload increases, and the fuel delivery requirements increase, the fueldelivery to the delivery injector may commence before the injector opensand continue while the injector is opened. In certain circumstances, allof the fuel may of course be metered into the delivery injector prior tothe opening thereof. These alternatives ensure that a sufficient amountof fuel is delivered to the engine cylinder for different operatingconditions. A fuel injector or other fuel metering means such as apositive displacement pump means may be used to supply fuel to thedelivery injector.

The fuel metering means may deliver the fuel at a pressure sufficient todeliver the fuel through the delivering injector when open directly tothe cylinder.

The operation of the delivery injector(s) and/or fuel injector or fuelmetering means may be controlled by an Electronic Control Unit (ECU).Engine control systems utilising such ECUs are described in standardtexts such as “The Motor Vehicle, twelfth edition (1996)” by K. Newton,W. Steeds and T. K. Garret and published by the Society of AutomotiveEngineers. Therefore, as the use of ECUs in engine control systems iswell known to persons skilled in this art, the ECU will not be describedherein in any detail.

The compressed gas supply means may include an air rail to whichcompressed gas may be delivered from the air compressor, and from whichcompressed gas is supplied to the delivery injector(s). Conveniently,the loss or reduction of the compressed gas supplied to the deliveryinjectors may be determined by sensing the pressure within the air rail.For example, a pressure sensor may be suitably located to measure thepressure within the air rail. The ECU may initiate the control methodwhen the air rail pressure falls substantially below a required supplypressure indicating a loss or significant reduction in the gas supply tothe air rail or a significant leak or break somewhere in the air supplymeans. Other means for determining the loss or a reduction in thecompressed gas supply are however also envisaged. For example, an airflow sensor could be provided in an air line between the air compressorand the air rail. Further, a suitable sensor may be provided within theair compressor to indicate whether it is operating satisfactorily ornot.

The method according to the present invention is particularly applicableto direct injected engines but may also have applications to certainmanifold injection engines.

Further the method may be used on engines having single or multiplecylinders. Where the method is used on a multi-cylinder engine, themethod may be used on one or more of the cylinders if not all of thecylinders.

The method according to the present invention can therefore provide a“limp home” mode of operation for the engine if there is a loss orsignificant reduction of the compressed gas supply to the dual fluidfuel injection system.

The method according to the present invention is particularly applicablefor four stroke engines where there is little possibility of the fuelbeing lost through the exhaust port(s) during the intake stroke. It ishowever also envisaged that the present invention may be adapted for useon two stroke engines.

It will be convenient to describe the present invention with referenceto the accompanying drawings which show a preferred embodiment of acontrol method according to the present invention. Other arrangements ofthe invention are however possible, and consequently, the particularityof the accompanying drawings is not to be understood as superseding thegenerality of the preceding description of the invention.

In the drawings:

FIG. 1 is a cross-sectional view of an internal combustion engine havinga

fuel and air rail unit mounted thereon;

FIG. 2 is a partial cross-sectional view of a fuel and air rail unit;and

FIG. 3 is a flow diagram showing a preferred embodiment of a method of

operating a dual fluid fuel injection system according to the presentinvention.

FIG. 1 shows a direct injected four stroke internal combustion engine 20comprising a fuel injection system, the engine 20 having an air intakesystem 22, an ignition means 24, a fuel pump 23, and a fuel reservoir28. An air compressor 29 is operatively arranged with respect to theengine 20 and typically driven off the engine crankshaft 33 by way of asuitable belt (not shown). Mounted in the cylinder head 40 of the engine20 is a fuel and air rail unit 11. The fuel pump 23 draws fuel from thefuel reservoir 28 which is then supplied to the fuel and air rail unit11 through a fuel supply line 55. Conventional inlet and exhaust valves15 and 16 are also mounted in the cylinder head 40 in the known mannertogether with conventional cam means 17 for actuating the valves 15, 16.The valves 15, 16 are arranged to open and close corresponding inlet andexhaust ports 18 and 19 for admission of fresh air and the removal ofexhaust gases from the cylinder in the known manner.

Referring now to FIG. 2, there is shown in detail a fuel and air railunit 11 which, whilst being different in design from that shown in FIG.1, shares all the same components thereof. The fuel and air rail unit 11comprises a fuel metering unit 10 and an air or delivery injector 12 forthe or each cylinder of the engine 20. The fuel metering unit 10 iscommercially available and requires no detailed description herein.Suitable ports are provided to allow fuel to flow through the fuelmetering unit 10 and a metering nozzle 21 is provided to deliver fuel toa passage 120 and thence to the air injector 12. The body 8 of the fueland air rail unit 11 may be an extruded component with a longitudinallyextending air duct 13 and a fuel supply duct 14.

As best seen in FIG. 1, at appropriate locations, there are providedconnectors and suitable ducts communicating the rail unit 11 with airand fuel supplies: air line 49 communicating air duct 13 with the aircompressor 29; air line 53 providing an air outlet which returns air tothe air intake system 22; and fuel line 52 communicating the fuel supplyduct 14 and fuel reservoir 28 providing a fuel return passage. The airduct 13 communicates with a suitable air regulator 27 which regulatesthe air pressure of the compressed air provided by the air compressor 29to the air duct 13.

Referring again to FIG. 2, the air injector 12 has a housing 30 with acylindrical spigot 31 projecting from a lower end thereof, the spigot 31defining an injection port 32 communicating with the passage 120. Theinjection port 32 includes a solenoid operated selectively openablepoppet valve 34 operating in a manner similar to that as described inthe Applicant's U.S. Pat. No. 4,934,329, the contents of which arehereby incorporated by reference. As seen in FIG. 1, energisation of thesolenoid in accordance with commands from an electronic control unit(ECU) 100 opens the valve 34 to deliver a fuelgas mixture to acombustion chamber 60 of the engine 20. However, it is not intended tolimit the valve construction to that as described above and othervalves, for example, pintle valve constructions, could be employed. Theelectronic control unit (ECU) 100 typically receives signals indicativeof crankshaft speed and air flow from suitably located sensors withinthe engine (not shown). The ECU 100, which may also receive signalsindicative of other engine operating conditions such as the enginetemperature and ambient temperature (not shown), determines from allinput signals received the quantity of fuel required to be delivered toeach of the cylinders of the engine 20. As alluded to hereinbefore, thisgeneral type of ECU is well known in the art of electronicallycontrolled fuel injection systems and will not be described here infurther detail.

The opening of each injector valve 34 is controlled by the ECU 100 via arespective communicating means 101 in timed relation to the engine cycleto effect delivery of fuel from the injection port 32 to a combustionchamber 60 of the engine 20. By virtue of the two fluid nature of thesystem, fuel is delivered to the cylinder entrained in a gas. Thepassage 120 is in constant communication with the air duct 13 via theconduit 80 as shown in FIG. 2 and thus, under normal operation, ismaintained at a substantially steady air pressure. Upon energisation ofthe solenoid of the air injector 12, the valve 34 is displaceddownwardly to open the injection port 32 so that a metered quantity offuel delivered into the air injector 12 by the fuel metering unit 10 iscarried by air through the injection port 32 into the combustion chamber60 of a cylinder of the engine 20.

Typically, the air injector 12 is located within the cylinder head 40 ofthe engine 20, and is directly in communication with the combustionchamber 60 defined by the reciprocation of a piston 61 within the enginecylinder. As above described, when the injection port 32 is opened andthe air supply available via the conduit 80 is above the pressure in theengine cylinder, air will flow from the air duct 13 through the passage80, passage 120 and, entrained with fuel, injection port 32, into theengine combustion chamber 60. Under normal operating conditions, thistypically occurs as the piston is moving towards its top dead centreposition during the compression stroke within the cylinder.

If however the compressed air supply from the air compressor 29 isinterrupted or significantly reduced due, for example, to a mechanicalfault in the air compressor 29 or to a break or leak in the air line 49or air rail 13, then the fuel and air rail unit 11 is no longer able tooperate in the manner described above. The control method according tothe present invention enables the engine to continue to operate undersuch circumstances to thereby provide a “limp home” mode of operation.

Referring to the flow diagram in FIG. 3, the air rail pressure (ARP) iscontinually monitored or periodically measured (step 201) to determinewhen there is any loss of or significant reduction in the air pressureto the fuel and air rail unit 11. If the air rail pressure is greaterthan or equal to a required air pressure level in the rail unit 11 (step202), then the fuel injection system operates in the normal manner (step208). If however the air rail pressure drops significantly below therequired pressure level, the ECU reacts to control the fuel injectionsystem according to the present invention, whereby the engine operatingconditions are determined (step 203) and the required fuelling rate isdetermined (step 204). A period and the timing of opening of thedelivery injector 12 to effect the required fuel delivery is thendetermined (step 205). This would typically be based on the prevailingengine speed/load which would determine when the injector 12 wasrequired to be opened in order to effect satisfactory fuel delivery tothe engine. As alluded to hereinbefore, this will typically correspondto a point when the pressure in the respective cylinder is less than thereduced pressure upstream of the delivery injector 12 and obviouslyprior to a point at which a subsequent combustion event will occur.Hence, this will most commonly equate to the intake stroke within thecylinder wherein the piston 61 is moving towards its bottom dead centreposition in the cylinder.

Hence, following the determination of the next engine cylinder toundergo an intake stroke therein (step 206), the delivery injector 12 ofthat cylinder is opened for the previously determined period at theselected timing, with the required amount of fuel previously determinedbeing supplied to the delivery injector 12 (step 207) during this openperiod thereof. As alluded to hereinbefore, the metered quantity of fuelmay of course be provided to the injector 12 prior to the openingthereof, partly before and partly during the open period thereof, orcompletely during the open period thereof.

The fuel metering unit 10 can in fact deliver the fuel at a pressuresufficient to deliver fuel through the delivery injector 12 directly tothe combustion chamber 60.

For example, the fuel metering unit 10 can supply the fuel during theperiod of opening of the delivery injector 12, particularly at lowloads. At higher loads, where a greater amount of fuel is required, thefuel metering unit 10 may commence or complete fuel delivery to thedelivery injector 12 prior to the opening thereof. The fuel meteringunit 10 is of course still able to accurately meter fuel as the fuelpressure is governed by the fuel pump 23 and any fuel regulation meansassociated with the fuel rail 14. The interruption or reduction of thesupply of compressed air will generally not affect the operation of thedelivery injector 12.

By virtue of the fact that the delivery injector 12 is opened at a timewhen the pressure in the cylinder is lower than the reduced orunsatisfactory air pressure upstream of the delivery injector 12 (i.e.in the air rail 13), fuel is drawn into the cylinder by way of thepressure differential existing across the delivery injector 12. Further,by controlling the timing of the opening of the injector 12, sufficientair may be drawn through the open injector 12 to provide for asatisfactory level of atomisation and entrainment of the meteredquantity of fuel.

Further, measures may be taken to ensure that the differential pressureacross the delivery injector 12 is always at a suitable level. Forexample, where the engine 20 is controlled by way of a drive by wire(DBW) system, the main throttle value of the engine 20 may be controlledso as to not permit a wide open throttle (WOT) setting whilst the methodaccording to the present invention is being used. In this way, anincreased level of vacuum may be generated during the intake stroke ofthe four stroke engine and have a greater differential pressure will becreated across the open delivery injector 12.

In regard to the required pressure level as discussed in reference tostep 202, for certain engine applications this does not necessarily needto equate to the predetermined or desired air pressure at which the fuelinjection system normally operates. That is, whilst the fuel injectionsystem will typically be arranged to operate with a particular airpressure level as controlled by the regulator 27, the fuel injectionsystem may in fact be able to satisfactorily operate when the airpressure is within a certain range below this predetermined air pressurelevel. Accordingly, the required pressure level as referred to inreference to step 202 at which the method according to the presentinvention will come into effect may not necessarily be the same as thenormal predetermined operating air pressure for the fuel injectionsystem. Instead, it may be set at some predetermined margin below thisnormal or desired system operating air pressure. In this way, a limphome mode of operation will not be instituted in cases where thepressure is just slightly below the normal operating air pressure forthe system. For example, whilst the normal system air pressure may besay 600 Kpa, the required pressure level below which the engine iscontrolled by the method as described may be set at say 400 Kpa.

The method according to the present invention is particularly applicablefor four stroke engines. It is however also envisaged that this methodcould be used on two stroke engines. The invention is equally applicableto single cylinder configurations and multi-cylinder engines of anynumber of cylinders. Further, the method according to the presentinvention is particularly applicable to direct injected engines, but mayalso be adapted to operate on manifold injected engines.

For example, if the injector 12 was arranged immediately upstream of theinlet port 18, the vacuum within the cylinder during the intake strokecould be used to draw fuel and air from the delivery injector 12,through the open inlet port 18 (as the valve 15 would be opening port 18during the intake stroke so as to allow fresh air for subsequentcombustion to be drawn into the cylinder) and hence into the combustionchamber 60 for subsequent ignition. Hence the opening of the injector 12in such an alternative system would require to be timed with respect tothe openirig of the inlet port 18 by the inlet valve 15.

Modifications and variations as would be deemed obvious to the personskilled in the art are included within the ambit of the presentinvention.

The claims defining the invention are as follows:
 1. A method ofcontrolling a dual fluid fuel injection system of an internal combustionengine having at least one cylinder, the fuel injection system having atleast one delivery injector and a compressed gas supply means forsupplying gas to the at least one delivery injector, the methodincluding: determining if there has been a reduction in the compressedgas supplied to the at least one delivery injector below a requiredsupply level; opening the at least one delivery injector when there is adepression in a respective said cylinder such that the pressure withinsaid cylinder is lower than the pressure upstream of the deliveryinjector if the compressed gas supply is below said required supplylevel; and delivering fuel to the delivery injector such that the fuelis drawn into the cylinder by virtue of the pressure differentialexisting across the delivery injector.
 2. A method according to claim 1,wherein the delivery injector injects fuel directly into a respectivesaid cylinder.
 3. A method according to claim 1, including controllingthe duration of opening of the delivery injector.
 4. A method accordingto claim 1, including controlling the start of opening of the deliveryinjector.
 5. A method according to claim 1, including opening thedelivery injector when the cylinder is undergoing an intake stroketherein.
 6. A method according to claim 1, including opening thedelivery injector when there is a vacuum induced in the cylinder.
 7. Amethod according to claim 1, including delivering fuel to the deliveryinjector at least in the period when the delivery injector is opened. 8.A method according to claim 1, including commencing the fuel delivery tothe delivery injector before the injector opens and continuing the fueldelivery while the injector is opened.
 9. A method according to claim 1,including delivering all of the fuel to the delivery injector prior tothe opening thereof.
 10. A method according to claim 1, includingdelivering all of the fuel to the delivery injector after the openingthereof.
 11. A method according to claim 8 wherein the fuel is suppliedto the delivery injector by a fuel metering unit at a pressuresufficient to deliver the fuel through the delivery injector when opendirectly to the cylinder.
 12. A method according to claim 1, wherein thecompressed gas supply means includes an air rail to which compressed gasis delivered from an air compressor and from which compressed gas issupplied to the delivery injector, the method including sensing thepressure within the air rail and initiating the control method when theair rail pressure falls substantially below the required supply level.13. A method according to claim 1, wherein the compressed gas supplymeans includes an air rail to which compressed gas is delivered from anair compressor and from which compressed gas is supplied to the deliveryinjector, the method including sensing the air flow within a gas linebetween the compressor and the air rail and initiating the controlmethod when the air flow falls substantially below a predeterminedlevel.
 14. A method according to claim 1, wherein the compressed gassupply means includes an air rail to which compressed gas is deliveredfrom an air compressor and from which compressed gas is supplied to thedelivery injector, the method including sensing the operation of the aircompressor and initiating the control method when the air compressor isnot operating satisfactorily.
 15. A method according to claim 1, whereinthe engine is a four stroke engine.